Göttingen 2025 – wissenschaftliches Programm

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P: Fachverband Plasmaphysik

P 17: Poster Session II

P 17.36: Poster

Mittwoch, 2. April 2025, 16:15–18:15, ZHG Foyer 1. OG

The role of turbulence and radial electric field in the achievement of high-performance regimes in W7-X — •Bojana Stefanoska¹, Daniel Carralero², Teresa Estrada², Thomas Windisch³, Emmanouil Marakoudakis², José Luis Velasco², and the W7-X team³ — ¹Max Planck Institute for Plasma Physics, 85748 Garching, Germany — ²Laboratorio Nacional de Fusion. CIEMAT, 28040 Madrid, Spain — ³Max Planck Inst. for Plasma Physics, 17491 Greifswald, Germany

Prolonged operation of the NBI system during the 2023 W7-X campaign refined a high-performance scenario combining NBI and ECRH heating. The NBI+ECRH high-performance (HP) phase exhibits a substantial increase in ion temperature and plasma energy. To study this scenario, the Doppler reflectometry (DR) system was upgraded with an E-band reflectometer, enabling core measurements of density fluctuations and the radial electric field E_r in high-density discharges.

DR measurements show that density fluctuation amplitude decreases as a strong density gradient builds during the pure NBI phase. The strong dependence of turbulence amplitude on the gradient ratio η_i indicates ITG-like turbulence in the core. E_r profiles remain flat before the HP phase and form a strong negative E_r well during it, accurately predicted by neoclassical simulations. Further turbulence reduction is observed in the HP phase, correlating with regions of strong radial electric field. These findings highlight the role of high density gradients in suppressing ITG-like turbulence, enabling improved performance with additional heating.

Keywords: W7-X stellarator; high performance; Doppler Reflectometry; core turbulence